Conventionally, various electric components such as a power window motor and a door lock device are mounted in a sliding door of a vehicle. As a wire holding structure for holding in the body of a vehicle wires connected to the vehicle sliding door, which is actuated to selectively open and close, and connected to electric components mounted in the sliding door, a structure having a holding member formed by joining an upper holding member and a lower holding member each formed of a plastic material, for example, is known. Wires are held in the holding member and the holding member is fixed to the body of a vehicle. See, for example, Patent Document 1. In a wire holding structure described in Patent Document 1, a corrugated tube accommodating a plurality of wires (harnesses) is rotationally held in the holding member such that the wires move in correspondence with opening/closing of the vehicle sliding door, or, in other words, with improved responsiveness. The holding member is fixed to, for example, a step member, which is arranged adjacently to the sliding door, at the rear end of the step member with respect to the vehicle using screws. See, for example, Patent Document 2.